Item

Abstract

The South Pacific Gyre (SPG) covers 10% of the ocean's surface and is
often regarded as a marine biological desert. To gain an on-site
overview of the remote, ultraoligotrophic microbial community of the
SPG, we developed a novel on-board analysis pipeline, which combines
next-generation sequencing with fluorescence in situ hybridization and
automated cell enumeration. We tested the pipeline during the SO-245
"UltraPac" cruise from Chile to New Zealand and found that the overall
microbial community of the SPG was highly similar to those of other
oceanic gyres. The SPG was dominated by 20 major bacterial clades,
including SAR11, SAR116, the AEGEAN-169 marine group, SAR86,
Prochlorococcus, SAR324, SAR406, and SAR202. Most of the bacterial
clades showed a strong vertical (20m to 5,000 m), but only a weak
longitudinal (80 degrees W to 160 degrees W), distribution pattern.
Surprisingly, in the central gyre, Prochlorococcus, the dominant
photosynthetic organism, had only low cellular abundances in the upper
waters (20 to 80 m) and was more frequent around the 1% irradiance zone
(100 to 150 m). Instead, the surface waters of the central gyre were
dominated by the SAR11, SAR86, and SAR116 clades known to harbor
light-driven proton pumps. The alphaproteobacterial AEGEAN-169 marine
group was particularly abundant in the surface waters of the central
gyre, indicating a potentially interesting adaptation to
ultraoligotrophic waters and high solar irradiance. In the future, the
newly developed community analysis pipeline will allow for on-site
insights into a microbial community within 35 h of sampling, which will
permit more targeted sampling efforts and hypothesis-driven research.
IMPORTANCE The South Pacific Gyre, due to its vast size and remoteness,
is one of the least-studied oceanic regions on earth. However, both
remote sensing and in situ measurements indicated that the activity of
its microbial community contributes significantly to global
biogeochemical cycles. Presented here is an unparalleled investigation
of the microbial community of the SPG from 20- to 5,000-m depths
covering a geographic distance of similar to 7,000 km. This insight was
achieved through the development of a novel on-board analysis pipeline,
which combines next-generation sequencing with fluorescence in situ
hybridization and automated cell enumeration. The pipeline is well
comparable to onshore systems based on the Illumina platforms and yields
microbial community data in less than 35 h after sampling. Going
forward, the ability to gain on-site knowledge of a remote microbial
community will permit hypothesis-driven research, through the generation
of novel scientific questions and subsequent additional targeted
sampling efforts.